Hindawi e Scientific World Journal Volume 2019, Article ID 3814962, 7 pages https://doi.org/10.1155/2019/3814962

Research Article Floods of 18 and 19 November 2016 in Batouri (East ): Interpretation of the Hydro-Meteorological Parameters and Historical Context of the Post-Event Survey Episode

Paulin Sainclair Kouassy Kalédjé ,1 Jules-Rémy Ndam Ngoupayou,1 Alain Fouépé Takounjou,2 Mireille Zebsa,3 Felaniaina Rakotondrabe,4 and Joseph Mvondo Ondoa1

1 Faculty of Science, University of Yaounde1,Yaound´ e-Cameroon,P.O.Box:812Yaound´ e,´ Cameroon 2Hydrological Research Centre, Institute of Geological and Mining Research, Yaounde,´ Cameroon 3Research and Innovation Centre, Ministry of Scientifc Research and Innovation, , Cameroon 4Advanced School of Engineering of Antananarivo, University of Antananarivo, Antananarivo, Madagascar

Correspondence should be addressed to Paulin Sainclair Kouassy Kaledj´ e;´ [email protected]

Received 25 September 2018; Revised 12 November 2018; Accepted 18 November 2018; Published 1 January 2019

Academic Editor: Federico Porcu

Copyright © 2019 Paulin Sainclair Kouassy Kaledj´ e´ et al. Tis is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

During the night of November 18 to 19, 2016, many stormy cells are not very mobile organized on the east of the southern plateau of Cameroon and dumped up to 260 mm of rain in 4 hours. Occurring on a relatively saturated soil, these rains caused strong foods of and Doume.´ Te foods were particularly damaging in the city of Batouri, where a subdivision was submerged by the Boumbe´ (tributary of the Sangha) with water heights in the houses reaching 1.75 m, despite the presence of a dam allowing clipping foods upstream of the basin. In this article, we present the results of the analysis of the postevent survey generated on this event with fow rates estimated on 15 sections of ungauged subbasins. Tese fows are then compared with those obtained from other recent postevent survey and those estimated by various regional estimations. Te inventory of heavy rains around Batouri during the period 1970-2016 has led to the revision of current development standards in the region, which seem to underestimate rainfall and infrequent fows.

1. Introduction exceptional events from the food leashes and the testimony of local residents. Tese operations have notably helped to Te intense rains accompanied by fash foods are one of reevaluate extreme fows in the Mediterranean and tropical 3 2 2 the characteristics of the Equatorial Guinean climate. Te zones, where values greater than 20 m /s/km over a few km extension of urbanized areas in southeastern Cameroon has have frequently been observed [3, 7]. multiplied homes vulnerable to fooding [1–3]. Te collection Te rain that hits the southeast of Cameroon on 18 and of data on fash foods is therefore a crucial issue for the 19 November 2016 had the particularity of reaching in some defnition of food zones and risk control in urban or peri- localities more than 200 mm in 3 hours, with a relatively 2 urban areas. In recent years, the practice of postevent survey small spatial extension, a few hundred km in total, and ofen (REX) has grown considerably in Europe and West Africa [4– only a few dozen square kilometers for the most intense 6] to evaluate fows of these extreme foods. Te purpose of part. Tis phenomenon is not new in the region, but its the REX analysis is to reconstruct the fows achieved during location in urbanized areas has led to very signifcant damage. 2 Te Scientifc World Journal

Figure 2: Precipitation casts from November 18, 2016 at 4:00 am GMTto19November2016at6:00amGMT,estimatedfromthe Panthere radar product (lef) and OHM-CV reanalysis (right).

Figure 1: Location of the study site and major rivers. BoumbesubbasininKenzouhasthefollowingpercentages´ [11]: scrubland 12%, forests 57%, agricultural land 24%, and urban areas 7%. Kadey has fairly similar percentages, but for Te characteristics of this episode are described in this thetwobasins,theareaafectedbythecumulativehighsis article. Flow rates were estimated a posteriori on eighteen on the immediate periphery of Batouri; the percentage of (18) sections of ungauged rivers. Te values obtained were urbanized area is higher and is around 25%. For the locality compared with those of other recent postevent survey from of Batouri, the percentage of urbanized area is close to 100%. the Southern Cameroon forest. Te return periods of the Te event of November 18 and 19 occurs in a particular episode were qualifed by a regional approach consisting of hydrological context, as two episodes of heavy rainfall hit the inventorying similar episodes that occurred in the vicinity of area the previous month. On October 12th, the stormy rains Batouri during the last 50 years. In addition to this article, mainly afect the south-south sector of the eastern region of information on this phenomenon can also be found in other Cameroon: Bertoua, , or Batouri are about 167 mm studies conducted by CEREMA (Center for Studies and and Mbang (south of the city) only 383 mm. Ten, on October Expertise on Risks, the Environment, Mobility and Devel- 25, a new episode touches Batouri with 307 mm in 12 hours opment)(2015)[8],usingthesamefowestimationmethod in Tripano. Te southeast Cameroon receives during this presented here, or by Rey et al. (2016) [9], which describe the episode142mminBertouaand122mminMandjou.On environmental consequences of such a hydrometeorological 18 November, the soils are very humid, the Kadey cracked episode. basins on the sources of Dem and Lom; Kadey has a fow rate 3 of 0.98 m /s, while the low fow rate before 12 October was 3 2. Materials and Methods 0.07 m /s. 2.1. Characterization of the Area. Te area afected by the intense rains of 18 and 19 November 2016 is located in 2.2. Meteorological Event. On November 18, 2017, the rains southeastern Cameroon. Te most impacted villages were started around 9:00 pm (6:00 pm GMT). Te results obtained from west to east: Sandae, Dogbwe, Batouri, Mongonam, from the weather radar images of France show little mobile Mboscoro, Kambel´ e´ III, and Dem (Figure 1). storm cells that have been stationed for about 4 hours in the Te area is drained by two rivers: Kadey in the West and area from Tongo Gadima in the southwest to Tikondi in the Boumbe´ in the East. Kadey has a fairly extensive catchment northeast, about twenty km, whose width does not exceed 7- 2 in the northwest (251 km ) but has had little impact during 8 km. From the analysis of these images, we see that, later in this episode. For the Boumbe,´ the topographic basin at the the night, other cells afected the entire Kadey department, 2 Kenzou station is 109 km . Te hydrogeological catchment, between the locality of Mbang and that of Pana, with lower on a cracked base, feeding the source of the Boumbecovers´ intensities. 2 372 km [10]. Te rapid recharge area of this catchment is Radar images provide an estimate of rainfall and their located north of a ridge and was only slightly afected by the spatial variability (Figure 2). Te Panther radar rain, supplied event. by Met´ eo-France,´ has been corrected for rain gauges using a correction factor, constant in space and updated every hour. Te relief, which is a plateau, consists of small hills, and 2 the altitudes vary between 780 and 1000 meters. Metamor- Te spatial resolution is 1 km and the temporal resolution phic rocks are largely in the majority but this sector has is 5 mm. Te radar rain OHM-CV (Mediterranean Hydrom- some karstic outcrops, the latter being located more to the eteorological Observatory Cevennes-Vivarais)´ corresponds northwest. Land use is made up of scrubland, areas, and to a reanalysis with a variable correction factor in space, 2 urbanized areas dominated by forest and mining structures interpolated by kriging. Te spatial resolution is 1 km and that have been expanding rapidly in recent decades. Te the reanalysis is available at a time resolution of 60 minutes. Te Scientifc World Journal 3

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0 0 Figure 3: Equipment of the station of Kadey with Batouri in 6h4h2h24h22h20h18h16h14h12h10h8h6h automatic station. Hourly rains Cumulated rains Te images difer between Batouri and Kenzou, a sector where Panther totals are underestimated compared to OHM- Figure 4: Hyetogram of the rain at the pixel that provided the CV totals. According to the OHM-CV reanalysis, the accu- maximum rain, at Batouri, from 18 November at 6:00 am GMT to mulations are of the order of 280 mm in the commune of 19 November at 6:00 am GMT. Batouri and 265 mm in the commune of Kenzou. According to this same treatment, the areas corresponding to rainfall 3 2 totals greater than 100, 150, and 200 mm are, respectively, specifc discharge is 5.6 m /s/km for a catchment with an 2 2 264, 123, and 67 km . Te OHM-CV radar rains are closer area of 102 km . Several testimonies concerning the water to the ground-based rainfall than the Panther radar rains, levelsontheroadindicateneverthelessthatthefoodofMay particularly in Mandjou and Kenzou. It is the consequence 12, 2001, was as important as that of November 19, 2016, at the confuence Boumbe-Kadey.´ of the treatment that spatially interpolates the diference 3 Furtherdownstream,thefoodreaches499m/s at between radar rain and values of the rains obtained by 2 Kambel´ e´ III on Boumbe,´ for a catchment area of 115 km , pluviometers on the level of the ground (Figure 3), while 3 2 the correction of radar rain is spatially uniform in the case i.e., a specifc fow of 4.3 m /s/km . According to the station’s of Panther. We will fnally retain the OHM-CV rains as a records and the food markings installed by the Hydrological Research Centre, the food of 19 November 2016 is of the reference. 3 Te rainfall hyetograph made from hourly and cumula- same order of magnitude as those of 1976 (519 m /s), 2005 3 3 tive rainfall data then shown in Figure 4 for the pixel provided (487 m /s), and 2003 (440 m /s). Te food of October 2016 3 maximum rainfall accumulation in the Kadey department. reached 344 m /s. Te return period of the November 2016 food seems to be between 10 and 20 years old. Tis moderate 3. Results and Discussions return period is clearly due to the fact that the rainy system has saved signifcant portions of the catchment area. 3.1. Hydrometric Stations of the Measurement Network. On the Kadey, at the Batouri station, in service since 1978, 3 Boumbe´ and Kadey have several hydrometric stations. On the thefoodreached234m/s and was only exceeded by the 3 Kadey, the city of Batouri has three stations, but not gauged 2003 food (254 m /s). Further upstream, at Dem, over the and whose data are not disseminated. On the Boumbe,´ two last 100 years, only the 1957 food is higher than the 2016 food other stations managed by the Regional Direction for the mark. In this sector, the return period of the food is certainly Environment, Planning and Housing (DREAL) are active, but greater than 20 years, but it is difcult to be more precise in are located downstream of Borgeneandarelessrelevantfor´ the absence of reliable data. It should be kept in mind that the this event. fows on the Bertoua, Batouri, and Kenzou stations are widely Te ordinary fows observed at the BoumbeandMbang´ extrapolated and that their absolute values are very uncertain. springareexplainedbytheabsenceofintenserainfallinthe Garou Boula¨ı-Gado Badjere-Boulembe-Mbang´ sector, which 3.2. Flow Estimation by Postevent Survey. To complete the isthefastrechargeareafortheBoumbe´ and Lom springs. hydrometric information on the ungauged watersheds, the TefowobservedontheDREALthresholdofthe fows were estimated afer the foods, by identifying the Boumbe´ spring is the sum of the outfow of the basin and the 2 maximum levels reached and the slopes of the water lines, fow on a small catchment of 1.02 km . If we subtract the input 3 then applying hydraulic formulas (Gaume and Borga, 2008). from the Boumbespring(11m´ /s), the fow corresponding 3 In a typical case, it is a question of choosing a rectilinear to this basin is exceptional, 36 m /s, i.e., a specifc discharge rectangle without modifcation of width or break of slope, 3 2 of 35.6 m /s/km .TesourceoftheBoumbeislessthanone´ tomeasurethecrosssectionatthepointconsideredand kilometer from the weather station of Pana. the slope of the water line on a few meters or a few tens of 3 At the Bertoua station, the Lom food (479 m /s) is the meters upstream and downstream of the cross section, fnally strongest in the last 10 years of the station’s existence. Te to apply a Manning-Strickler hydraulic formula to calculate 4 Te Scientifc World Journal the fow velocity, the roughness coefcient being estimated 1000 according to the size of the bed. In other cases, weir-type formulas are applied to water heights estimated at thresholds, 100 or the velocity is estimated by applying the Bernoulli theorem between the upstream and downstream coasts of a structure

under load, bridge, or nozzle. Flow (m3/s) 10 In addition to the two stations located on Boumbeand´ Lom, fows were estimated for eighteen (18) sections. One 1 of the sections (Batouri) corresponds to the threshold of a 0.1 1 10 100 1000 reservoir and the fow rate was calculated by a weir formula Surface (Km2) with a thick threshold, with rectangular section without ridges, in the free regime. Te fows of the other sections Figure 5: Probable fows based on catchment area. were estimated from the Manning formula. Te calculation method is detailed in other lessons learned from rivers in 3 EuropeandWestAfrica[5,12,13].Te2016foodsurveys Qm /srare=30×S(km)0, 75 and spreadsheets are available in the Ministry of Scientifc Research and Innovation database through the Hydrological (ii) Crupedix: Research Centre. 3 Outstanding Qm /s = Q10 years × K2 Te areas of the basins corresponding to these sections 3 were calculated by treatment of the Digital Elevation Models Qm /s(10 years)=S(km2)0, 8×(P(mm)/80)2× (DEM) 25 m of the National Geographic Institute (NGI). K Te mean water slides, by correlations and corrections, were calculated for each basin by processing the radar image Teestimatedfowsareofthesameorderofmagnitudeas provided by the OHM-CV. those observed during other French REX in the Mediter- Te fows are expressed in terms of probable fow rates, ranean region: around Draguignan in the Var in 2010 [5, framed by lower and upper bounds corresponding to the 14], on the Coteˆ d’Azur around Mandelieu in 2015 [13], and uncertainties on the estimation of these fows. Tese uncer- around Abidjan in 2013 [15] and Grand Bassam in 2012 [16]. tainties vary from 20 to 50% according to the choice of the Tey remain signifcantly lower than those estimated during theGardfoodsin2002,atleastforbasinslargerthanafew section, its regularity, and the legibility of the food traces. 2 Te most important uncertainty factor is ofen related to the km ,oraroundLodevein2015fornonkarstbasins[17].Itis` estimation of the Strickler roughness coefcient. also noted that the estimated feedback values for the episode 3 2 Tespecifcfowsvarybetween4and27m/s/km .Te of November 18 and 19, 2016, exceed the exceptional fows 3 2 3 highest values (Pana, 29.8 m /s/km , and Batouri, 26.3 m /s/ calculatedbytheCrupedixformulaproposedforexceptional 2 fows, while remaining below those given by the Bressang- km ) correspond to the two smaller basins, less than or 2 Golossofrare.Itispossiblethatthedecadalrainfallquantile equal to 1 km . For the other basins, the specifc fows vary 3 2 in the area, P10 years = 122 mm, occurring in Crupedix is between 10 and 18 m /s/km , if one considers only the basins underestimated. having received more than 150 mm of rain. Te maximum 3 2 specifc discharge, 18 m /s/km , corresponds to the Batouri catchment,attheheartoftherainysystem.Tebasinswitha 3.4. Estimation of the Return Period of the Rains. Te only water slide of less than 150 mm have the lowest specifc fows, long series of intraday rains available around Batouri is the 3 2 from 1.4 to 7.5 m /s/km (Dem and Kambel´ e´ III sections Bertoua series, whose statistical analysis was done for the upstream of the catchment area of Boumbe),´ sections of the period 1968-2014 by the Hydrological Research Centre in Kadey incorporating an upstream little watered). Accounting 2017 [18]. Te return periods were calculated afer adjusting for the impact of pond area on fow abundance, probable fow for Weibull law has the observed data for a return period of rates are fairly well organized around 50 years; the estimates provided are 49 mm in 30 minutes, 2 72 mm in 1 hour, and 121 mm in 4 hours. ��3/� = 19,96 ����20.57 (� = 0,81) or ��3/� = 17,58 2 Te Simulation of Hydrograms for the predetermination �� 0.76 (� = ��2 0,85) if only pools over 150 mm in sizes are of foods REGionalized (SHYREG) method [19] based on the considered (Figure 5). synthesis of several hundred series of hourly rainfall and on a regionalization of the parameters from the daily rainfall 3.3. Comparison with Other Exceptional Episodes. Figure 5 in the Cameroonian territory provides higher accumulations compares the results obtained for the event of 18 and 19 for durations less than 1 h, but close enough for longer November 2016 (considering only basins that received more durations: according to National Direction of Meteorology than 150 mm of rain) with other exceptional episodes since (2014) [20, 21], for the same period of return, ffieth year, 2000 in southeastern Cameroon. Debit estimates provided by we would have accumulations of the order of 70 mm in 1 regional food discharge prediction formulas are also shown: hour, 90 mm in 2 hours, and 120 mm in 4 h. For a 100-year return period, the estimates are of the order of 90 mm in 1 h, (i) Bressang-Golossof (for catchments area between 20 100mmin2h,120mmin3h,and135mmin4h.According 2 and 400 km ): to these estimates, the one-time maximum of the episode Te Scientifc World Journal 5

10000 300 280 1000 260 240 /s)  220 100 200

Flow (m Flow 180 10 Water slide (mm) Water 160 140 1 120 0.1 1 10 100 1000 0 25 50 75 100 125 150 175 200  Surface of catchment area (Km ) Surface (Km) Batouri (18-19 Nov Gard 2002 1971 1993 Lodève 2015 BG rare 1976 nov-16 Var 2010 Crupedix exc Cête d'Azur) 1979 2007 Figure 7: Spatial extension of exceptional episodes exceeding Figure 6: Comparison of fows obtained for diferent recent 200mmin4hours. postevent survey and for diferent food predetermination estima- tion.

Chaptal (1934) [23] mentions 227.9 mm fell in 24 hours on of November 18 and 19, 2016, would therefore have a return September 26 and 27, 1933 (with height of up to 33 mm in period well above the centennial. 15 minutes and 40 mm in 30 minutes, these intensities cited Tese estimates can be compared to the inventory as being remarkable were only rarely exceeded in 60 years, of exceptional episodes in the forest massif of southeast November 3, 1910, and July 8, 1917), and 233 mm in 7 h on Cameroon. Ndam Ngoupayou et al. (2014) [22] state as October 11, 1862. follows: Areas of water bursts exceeding diferent thresholds were calculated from interpolated rainfall or radar images (i)90mmin1houronOctober27,1984,inSongloulou. (Figure 7). We distinguish the much localized episodes for (ii)120mmin1houratNatchigalon30September2001. which the precipitated slide decreases rapidly according to the (iii) 180 mm in 2 hours at Goura on 25 October 1993. surface(1971,2007,and2016)andthoseforwhichitdecreases more slowly (1976, 1979, and 1993). For the frst group, the (iv)298mmin4hEbebdaand385mmin4hinBamend- areas corresponding to a water level of at least 200 mm vary 2 jin on 23 September 1997 (and not in October as the from 25 to 75 km , while for the second group, they exceed authors have indicated, no remarkable episode having 2 200 km . Te area of the water body exceeding 200 mm can occurred in this month). 2 beestimatedonaverageabout100km . Tese episodes could be mapped from the rainfall data A very crude reasoning can be used to try to determine availableintheNationalDirectionofMeteorologydatabases the local return period of an exceptional rainfall of at least 200 mm in 4 hours, whose spatial extension is, as we have at these dates. For the episode of September 23, 1997, it 2 should be noted that no cumulation available in the National seen, 100 km on average. During the period 1985-2016, there Direction of Meteorology database exceeds 300 mm, the are seven episodes of this type, on a fxed area that can be represented by a square of 50 km side. It is inferred that a total accumulations of Ebebda and Bamendjin from another net- 2 work of measurements. Te 1993 episode seems to be of a of 7 × 100 = 700 km receivedarainfallofatleast200mm diferent nature from the others, much larger, and more like a (in 4 hours) during the period considered, i.e., thirty-one Cevennes episode. But an intense rain cell, exceeding locally (31) years. For each point in the area to be averaged once 200mm, is also centered on the northeast of Batouri. with a rainfall of more than 200 mm in 4 hours, it would To these episodes are added three more intense episodes take 2,500/700 more time, or 2,500/700 × 45 = 111 years. (17 September 2007, 29 September 2016, and 18 November Te same reasoning, realized for a 150 mm water slide with 2 2016)ofmorethan200mminafewhours(3to5hours),for an average surface area of about 300 km , would lead to which we have radar rainfall (Figure 6). estimating the corresponding return period at around 45 Considering only the period 1985-2016, it is thus a total years. By comparison, the Simulation of Hydrograms for the of seven exceptional episodes which were observed on the predetermination of foods REGionalized (SHYREG) gives immediate periphery of Batouri, on an area delimited by this rain a substantially centennial return period. It would Kenzou to the north, Dem to the south, Mbam to the west, therefore tend to overestimate return periods [24–26]. and Nbounou to the East. Tese episodes have in common In this calculation, however, there are numerous uncer- to have exceeded locally 200 mm in less than 4 hours, which tainties, relative to the estimation of the reference area, the leadstoaperiodofregionalreturn(thatistosay,onthearea) average extent of a given water table, the assumption that of less than 7 years for this type of episode. On earlier dates, the intense rainfall is equiprobable over the reference area, 6 Te Scientifc World Journal the number of undetected intense episodes, the short length remain, the return period of rain received by the Kadey of the reference period with regard to the validity of the BasininBatouricouldbebetween60and160yearsold.In statistical analysis, and the spatial abatement allowing to the continuation of this article, a rain-fow model will be move from the occurrence of a rainfall height to a point to proposedtoevaluateintheframeworkofthesameepisode that of an average rainfall of the same height over a given the role of urbanization or the initial conditions of saturation area, which has not been taken into account. In this way, by of soils on the fows, as well as the efciency of the structures 2 choosing, for example, a smaller reference area of 900 km of storage for food protection. (a square of 30 km on the side), the return period of a water slide of 200 mm in 4 hours would be increased to 60 years Data Availability andthatofawaterslideof150mmin4hto20years.It is therefore appropriate to set a fairly broad range for the Te data of the present study are available but can not be return period of an episode such as that which afected the publishedyet,becausetheyarestillthepropertyofthe Kadey catchment, at least between 60 and 160 years of age, Ministry in Charge of Scientifc Research and Innovation of taking into account the uncertainties in the reference area Cameroon until December 2019. in the method used. In addition, the return period of the October 1998 episode in Pana, whose maximum seems to Disclosure have reached 420mm locally in 6:30, was estimated at a little over a hundred years, based on the historical information Tisstudywascarriedoutaspartofthehydrometeorological showing four other comparable episodes over the last 600 studies for the construction of a dam in eastern Cameroon. years [27]. Davy (1989) [28] also mentions that four showers greater than 200 mm in 6 hours were recorded at the Pana Conflicts of Interest station between 1889 and 1988. Tese episodes are referring to periods signifcantly longer than that of the November Te authors declare that they have no conficts of interest. 2016 rain in Batouri; the estimated return periods cannot be directly compared to those we estimated, but they do not Acknowledgments seem to invalidate the range we have proposed [29]. To answer more precisely the question of the frequency We would like to thank our colleagues from Hydrological of these rains with strong intensities on short durations Research Centre and Geochemical Analysis Laboratory of supposes more important studies. For example, using the Water who participated in the feld measurements. We also recent archives of radar data from 1990 to the present day thank Christelle Gislaine Belinga for the prospecting work of the Agency for the Safety of Air Navigation in Africa and carried out on Met´ eo-France,´ InfoClimat, and the National Madagascar (ASECNA) coupled with those of the National Meteorological Direction of Cameroon. Direction of Meteorology, it would be possible to study their frequency by taking into account both the area covered by the References high intensities and their duration. [1] E. Gaume and C. Bouvier, “Analyse hydro-pluviometrique des crues du Gard et du Vidourle des 8 et 9 septembre 2002,” La 4. Conclusion Houille Blanche, International Water Journal, no. 6, pp. 99–106, 2004. Teposteventsurveyonthefoodsobservedon18and19 [2] G.Delrieu,V.Ducrocq,E.Gaumeetal.,“Tecatastrophicfash- November 2016 on the southeast of the South-Cameroon food event of 8-9 September 2002 in the Gard Region, France: Plateau in Batouri precisely characterized the rains and afrstcasestudyfortheCevennes-Vivarais´ Mediterranean fows of this meteorological event. Rainfall accumulations hydrometeorological observatory,” JournalofHydrometeorol- of 260 mm in 4 hours have been achieved, and the specifc ogy,vol.6,no.1,pp.34–52,2005. fows are of the order of 10 to 20 m3/s/km2 or more. Tese [3]J.M.Masson,“Analysed’unelongueserie´ pluviographique - fows are of the same order of magnitude or exceeded by Montpellier Bel-Air 1920-1971,” La Met´ eorologie´ ,vol.20-21,pp. those estimated during other recent Cameroonian REX in the 105–117, 1980. forest and humid tropical regions (Congo Basin) on the one [4] E. Gaume and M. Borga, “Post-food feld investigations in handandontheotherhandinseveralregions:Montpellier- upland catchments afer major fash foods: proposal of a Grabels, Nimes, Var, and Lodeve` (France); Bouar, Kaga- methodology and illustrations,” Journal of Flood Risk Manage- bandoro, and Bosangoua (Central Africa Republic); Kano, ment,vol.1,no.4,pp.175–189,2008. Adamawa,Taraba,Oyo,DeltaImoLagos,andEdo(Federal [5]O.Payrastre,J.P.Naulin,C.C.Nguyen,andE.´ Gaume, Article RepublicofNigeria).Tistypeofepisodeisnotsorarein ID 01272025, Analyse hydrologique des crues de juin 2010 the Kadey and the repetition of these episodes encourages dans le Var. Rapport de recherche IFSTTAR, 33 p, en ligne : revising the management standards with regard to rare foods https://hal.archives-ouvertes.fr/hal-01272025/document. at the level of Cameroon but also of the subregions Central [6] P.Brunet, C. Bouvier, and E.´ et Gaume, “Retour d’experience´ sur Africa and Africa from west. Te estimates provided by les crues du Gard en septembre 2002 : controleˆ de la qualitedes´ the statistical analysis of the Batouri local series or by the debits´ estimes´ et comparaison avec les formules synthetiques´ SHYREG method seem to overestimate the return periods of regionales,”´ in Ev´ enements` extremesˆ fuviaux et maritimes, CD- the rains for intraday durations. Although large uncertainties Rom, congres` SHF,p.8,Paris,2012. Te Scientifc World Journal 7

[7] E. Gaume, V. Bain, P. Bernardara et al., “A compilation of data memoire´ hors-serie´ , pp. 77–91, Association des Geologues´ du on European fash foods,” Journal of Hydrology,vol.367,no.1-2, Sud-Est,RevuedeGeologie´ Alpine, 1990. pp.70–78,2009. [22] J. Ndam Ngoupayou, J. Dzana, A. Kpoumie et al., “Present- [8] CEREMA (2015) - Retour d’Experience´ des intemperies´ sur day sediment dynamics of the Sanaga catchment (Cameroon): les departements´ de l’Herault´ et du Gard de septembre a` from the total suspended sediment (TSS) to erosion balance,” decembre´ 2014. Rapport d’expertise sur la commune de Grabels. Hydrological Sciences Journal,vol.61,no.6,pp.1080–1093,2016. Edit.´ DDTM34 (DREAL Languedoc-Roussillon), 72 p., en ligne [23] L. Chaptal, “Les pluies de la fn septembre 1933 aMontpellier,”` : http://www.herault.gouv.fr/content/download/15944/102326/ Annales de l’Ecole´ National d’Agriculture de Montpellier,vol. fle/RapportExpertiseCerema GRABELS 2015 05 22.pdf. XXII, no. 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